> > It seems to always be (inserted_elements * 2) - 1. > > When adding 2 elements, it hashes 3 times. When adding 1 element, it > > only hashes once. What is happening here? Why is the hash calculated > > twice? What is so special about the last or first element? > > https://gcc.gnu.org/onlinedocs/libstdc++/manual/unordered_associative.html#containers.unordered.cache > answers part of the question (libc++ on the other hand seems to have > chosen always to cache the hash). > > The other part is related to how the elements are linked in the hash > table, note that the hashes computed are 0 1 0 2 1 3 2 4 3 5 4 6 5 7 > 6... Reading the code seems best to understand what is going on. > Thank you for the link to the documentation. That also explains why removing "noexcept" on the hash function enables caching. I will try to step through the code and understand it. Reading STL is always not so easy... Thanks for the pointers.
